Book stock against physical stock
Every fuel stock check is the same comparison. Book stock is what the records say should be in the tank: the opening stock, plus what tankers delivered, minus what the meters sold, plus any test fuel poured back. Physical stock is what the dip says is really there. The difference is your gain or loss.
| Step | Formula |
|---|---|
| Book stock | Opening + receipts − meter sales + test fuel returned |
| Variance | Closing dip stock − book stock |
| Variance % | Variance ÷ meter sales × 100 |
The percentage is taken against sales, not against what is in the tank, because that is how a loss is judged: how much product went missing for every litre you sold.
What a loss usually means
A small loss is normal. Petrol evaporates, and temperature changes the volume of fuel between a cool morning dip and a hot afternoon one. A loss larger than usual, or one that keeps growing, almost always has a cause you can find:
- A tanker delivered short, and it was not caught at decantation.
- A dispenser is delivering more than its meter shows (meter running slow).
- Test fuel was not returned to the tank, or was returned but not recorded.
- A dip was read wrongly, or the wrong calibration chart was used.
- A leak in the tank or pipeline. Treat a steady unexplained loss as a possible leak.
- Theft.
A gain is not good news either. It usually means a meter is running fast (customers are being short-delivered, which is a Legal Metrology problem), or a dip or a sale was recorded wrongly.
Read the full guide: evaporation and stock loss at a petrol pump.
Compare against your permissible limit
Oil companies set permissible limits for stock variation, and they differ between petrol and diesel. Use the limit in your oil company's current guidelines, not a number from the internet, and compare your monthly variance with it.
Frequently asked questions
Should I calculate stock loss daily or monthly?
Both. A daily check catches a problem the day it starts. A monthly total smooths out temperature swings and is the figure compared against permissible limits.
Why do I get a gain on hot days?
Fuel expands when it warms. If the closing dip is taken in the heat and the opening dip in the cool, the same fuel takes up more room. Over a month these swings largely cancel out.